1. Field of the Invention
The present invention relates to transmission/reception apparatuses and methods, capable of improving advantages of the CDMA (Code Division Multiple Access) system, etc. in a mobile communication system which is effective in satisfying conditions such as overcoming multi-path fading, improving transmission quality, improving frequency utilization efficiency and storing multi-rate information.
2. Description of the Related Art
Conventionally, access systems such as FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access) and CDMA are actually used in mobile communications. It is essential for these access systems to overcome multi-path fading, improve the transmission quality, improve the frequency utilization efficiency and store multi-rate information, etc., as described above, and the CDMA system is currently considered to be an effective system meeting these requirements.
The CDMA system is a system in which the transmitting side sends transmission information in frame units after multiplying it by a spreading code and the receiving side extracts the original transmission information by multiplying the received signal by the same spreading code.
FIG. 1 is a block diagram of conventional transmission/reception apparatuses. Here, the transmission/reception apparatuses are a base station and mobile stations (communication terminal apparatuses) of a mobile communication system, which is based on the CDMA system.
In FIG. 1, base station 1300 carries out radio communications with a first to third mobile stations 1301 to 1303. In this example, base station 1300 is provided with a communication circuit with three mobile stations and comprises their respective voice encoders 1310 to 1312, error correction encoders 1313 to 1315, modulators 1316 to 1318, spreaders 1319 to 1321, adder 1322, amplifier 1323, antenna 1324, matched filters 1325 to 1327, RAKE combiners 1328 to 1330, error correction decoders 1331 to 1333, and voice decoders 1334 to 1336.
First mobile station 1301 comprises antenna 1340, matched filter 1341, RAKE combiner 1342, error correction decoder 1343, voice decoder 1344, voice encoder 1345, error correction encoder 1346, modulator 1347, spreader 1348, and amplifier 1349.
Second mobile station 1302 comprises antenna 1350, matched filter 1351, RAKE combiner 1352, error correction decoder 1353, voice decoder 1354, voice encoder 1355, error correction encoder 1356, modulator 1357, spreader 1358, and amplifier 1359.
Third mobile station 1303 comprises antenna 1360, matched filter 1361, RAKE combiner 1362, error correction decoder 1363, voice decoder 1364, voice encoder 1365, error correction encoder 1366, modulator 1367, spreader 1368, and amplifier 1369.
In the mobile communication system configured as shown above, the following is an explanation of a case where transmission is carried out from base station 1300 to mobile stations 1301 to 1303.
First, for first mobile station 1301, base station 1300 carries out error correction encoding using error correction encoder 1313 on digital data created by voice encoder 1310, modulates the encoded data with error correction using modulator 1316 and multiplies it by a user-specific spreading code using spreader 1319.
Likewise, for second mobile station 1302, base station 1300 processes transmission data using voice encoder 1311, error correction encoder 1314, modulator 1317 and spreader 1320, and for third mobile station 1303, it processes transmission data using voice encoder 1312, error correction encoder 1315, modulator 1318 and spreader 1321.
Each spread signal is summed up in adder 1322, amplified in amplifier 1323 and emitted from antenna 1324.
In first mobile station 1301, a signal is received by antenna 1340 and only a desired signal is extracted by matched filter 1341, subjected to path diversity by RAKE combiner 1342, subjected to error correction decoding to improve the reception quality by error correction decoder 1343, and voice is reproduced by voice decoder 1344.
In second mobile station 1302, only the voice of a desired user is reproduced likewise using antenna 1350, matched filter 1351, RAKE combiner 1352, error correction decoder 1353 and voice decoder 1354. In third mobile station 1303, only the voice of a desired user is reproduced likewise using antenna 1360, matched filter 1361, RAKE combiner 1362, error correction decoder 1363 and voice decoder 1364.
Then, transmission from mobile stations 1301 to 1303 to base station 1300 is explained.
In first mobile station 1301, digital data created by voice encoder 1345 are subjected to error correction encoding by error correction encoder 1346, the encoded data with error correction are modulated by modulator 1347, given user-specific spreading in spreader 1348, amplified by amplifier 1349 and emitted from antenna 1340.
In second mobile station 1302, a signal is emitted likewise through voice encoder 1355, error correction encoder 1356, modulator 1357, spreader 1358, amplifier 1359 and antenna 1350. In third mobile station 1303, a signal is emitted likewise through voice encoder 1365, error correction encoder 1366, modulator 1367, spreader 1368, amplifier 1369 and antenna 1360. All these signals are emitted on a same frequency.
Base station 1300 receives signals transmitted from mobile stations through antenna 1324, extracts only the signal of first mobile station 1301 by matched filter 1325, carries out path diversity by RAKE combiner 1328 and error correction decoding to improve the reception quality by error correction decoder 1331, and reproduces voice by voice decoder 1334.
Likewise, base station 1300 extracts only the signal of second mobile station 1302 by matched filter 1326, carries out path diversity by RAKE combiner 1329 and error correction decoding to improve the reception quality by error correction decoder 1332, and reproduces voice by voice decoder 1335. Furthermore, base station 1300 extracts only the signal of third mobile station 1303 by matched filter 1327, carries out path diversity by RAKE combiner 1330 and error correction decoding to improve the reception quality by error correction decoder 1333, and reproduces voice by voice decoder 1336.
Thus, through CDMA transmissions, signals of mobile stations 1301 to 1303 are spread by different codes and superimposed on a same frequency. In this case, spreading allows a short de-lay time path to be separated, making it possible not only to eliminate influences of multi-path fading through RAKE reception but also to produce path diversity effects, improving the line quality.
Furthermore, the CDMA system can implement a uniform transmission quality for all mobile stations 1301 to 1303 and also allows adjacent cells to use a same frequency, possessing features such as high frequency utilization efficiency and easy multi-rate accommodation.
However, in the conventional transmission/reception apparatus above, carrying out RAKE reception requires accurate detection of fingers, that is, accurate detection of the fading status, delay wave status, etc., which takes considerable time.
Moreover, if at least one of a plurality of mobile stations fails in power control or has noise with great power over a narrow band, its interference may disable communications of all mobile stations within a cell or within peripheral cells.
The number of paths is also variable with time, which may prevent path diversity effects from being always obtained.
Bands available to the system are also restricted due to the chip rate which is the multiplication factor after spreading, limiting its implementation only to bands which are an integer times the bandwidth.
Furthermore, since many mobile stations use a same frequency band simultaneously, the scale of an interference cancellation apparatus introduced to increase their capacities is also increased.
Moreover, synchronization at a fast chip rate is required, but it is difficult to implement the function to establish such synchronization.
It is an objective of the present invention to provide a transmission/reception apparatus and method capable of eliminating waste time for accurate finger detection during RAKE reception, communication disabled state of all mobile stations within a cell due to radio interference among mobile stations, reduction of path diversity effect due to the number of paths variable with time, restrictions on introduction of the frequency band to the system due to restrictions on the band available to the system, expansion of an interference cancellation apparatus introduced to increase capacities, difficulties in establishing synchronization at a fast chip rate, etc.